222 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



simplicity of form in these cylindrical shells being accompanied by a correspond- 

 ingly simple form in the septa. It is noticeable that Hyatt makes no direct reference 

 to the septation in defining his sub-orders, families, and genera of the Nautiloidea 

 in Eastman's ' Translation,' but depends rather upon the nature of the septal 

 necks and the siphuncle and its contents, if any, taking into account likewise 

 characteristic ornamentation . 



The arrangement of the remaining groups of the Nautiloidea (exclusive of the 

 Actinoceratida3, CyrtoceratidaB, and Poterioceratidae) follows in the main that of 

 Hyatt's " Carboniferous Cephalopods," contributed to the ' Geology of Texas, 

 Fourth Annual Rep.' (1892), with such modifications as it became necessary to 

 make in the presence of the new material available. 



For the Ammonoidea, here represented by the Goniatites, Hyatt's widely recog- 

 nised classification has been adopted, though in the case of the largest and most 

 important group, the Glyphioceratidse, some changes have been introduced. Under 

 his original description of Glyphioceras Hyatt divided the genus into two sections 

 which he characterised, and to which he allotted certain species. To these unnamed 

 sections I have given distinctive names as sub-genera, and following Perrin Smith, 

 have resuscitated Muensteroceras, also as a sub-genus, taking the suture-line in each 

 case as the principal distinguishing feature (Synopsis of Families, Genera, etc., p. 219). 



The retention of Gastrioceras as an independent genus, rather than the 

 merging of it in Glypliioceras, as suggested by Karpinsky, 2 is held by Perrin Smith 

 to be justified by the fact that Gastrioceras being a later branch than Glyphioceras, 

 phylogenetic studies are facilitated by their separation, while there is no difficulty 

 in distinguishing typical members of each group. Gastrioceras is therefore main- 

 tained in accordance with this view. 



The most cursory survey of the material at present collected and recorded shows 

 plainly what a rich molluscan fauna is contained in the rocks of the Carboniferous 

 System spread over a great part of Ireland. It is a safe prediction that with more 

 workers in the field much additional material might be gathered in, thereby greatly 

 facilitating those studies which may lead to the most important results in all that 

 relates to the phylogeny of the Cephalopoda, and the important biological and 

 faunal questions they help to elucidate; for, as it has been truly stated, "the 

 Cephalopoda alone, of all animals, preserve in the individual a complete record of 

 their larval and embryonic history, the protoconch and early chambers being 

 enveloped and protected by the latter stages of the shell." 3 Hence the great 

 importance that must be attached to the collection of many individuals of the same 

 species to supply the means of carrying out such embryological work as has already 



1 ' Proc. California Acad. Sci.,' third ser., Geology, vol. i, No. 3, p. 105, 1897. 



- ' Mem. A.cad. [mp. Sci. St.. Pctersbourg,' vol. xxxvii, p. 48, 1889. 



3 J. Perrin Smith, in ' Proc. Anier. Phil. Soc.,' vol. xxxv, 1896, p. 254. 



